In an optoelectronic semiconductor device there are "photoactive" regions in which either emission or detection of photons can take place. Emission of photons takes place when an applied electrical current injects holes and electrons across a junction and the electrons and holes can combine in the photoactive region, the resultant energy being released in the form of photons. Detection of photons takes place when photons incident in the photoactive region create electronhole pairs, causing an electrical current to flow.
Silicon has an indirect band gap and this has hindered the development of acceptable silicon based photoemitters suitable for use in integrated silicon optoelectronic applications. Silicon's band gap is also high, hindering development of photodetectors sensitive to wavelengths of longer than around 1 .mu.m. Optoelectronic devices which are emissive of, or sensitive to, electromagnetic radiation of about 1.5 .mu.m, which is the basis of optical fibre systems, would be particularly significant in communications applications and in optical computing systems that are resistant to severe electromagnetic interference (EMI). The device architecture proposed by this invention permits such silicon-based optoelectronic devices to be made.
Several different approaches have already been investigated, with a view to developing a suitable photoemissive device which is capable of producing radiation at a wavelength of about 1.5 .mu.m from a silicon-based device.
In one approach SiGe superlattice-based structures have been developed making use of zone folding to produce a pseudo direct band gap. In another approach, silicon has been doped with erbium which has an internal transition energy equivalent to 1.5 .mu.m. However, neither of these approaches has led to a practical device.